feat(docs): add a `decisions` folder with ADR

An architectural decision record (ADR) is a document that describes a choice the team makes about a significant aspect of the software architecture they’re planning to build. Each ADR describes the architectural decision, its context, and its consequences. ADRs have states and therefore follow a lifecycle

docs/decisions/README.md

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+# Decision Log
+
+We capture important decisions with [architectural decision records](https://adr.github.io/).
+
+These records provide context, trade-offs, and reasoning taken at our community & technical cross-roads. Our goal is to preserve the understanding of the project growth, and capture enough insight to effectively revisit previous decisions.
+
+Get started created a new decision record with the template:
+
+```sh
+cp template.md NN-title-with-dashes.md
+```
+
+For more rational behind this approach, see [Michael Nygard's article](http://thinkrelevance.com/blog/2011/11/15/documenting-architecture-decisions).
+
+We've inherited MADR [ADR template](https://adr.github.io/madr/), which is a bit more verbose than Nygard's original template. We may simplify it in the future.
+
+## Evolving Decisions
+
+Many decisions build on each other, a driver of iterative change and messiness
+in software. By laying out the "story arc" of a particular system within the
+application, we hope future maintainers will be able to identify how to rewind
+decisions when refactoring the application becomes necessary.

docs/decisions/template.md

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+---
+# status and date are the only required elements. Feel free to remove the rest.
+status: {[proposed | rejected | approved | deprecated | … | superceded by [2021-01-01 Example](2021-01-01-example.md)]}
+date: {YYYY-MM-DD when the decision was last updated}
+based-on: {[Short Title](2021-05-15-short-title.md)}
+story: {description or link to contextual issue}
+---
+
+# {short title of solved problem and solution}
+
+## Context & Problem Statement
+
+2-3 sentences explaining the problem, and what are the forces influencing the decision.
+<!-- The language in this section is value-neutral. It is simply describing facts. -->
+
+## Priorities & Constraints <!-- optional -->
+
+* {list of concerns}
+* {that are influencing the decision}
+
+## Considered Options
+
+* Option 1: Thing
+* Option 2: Another
+
+## Decision Outcome
+
+Chosen option [Option 1: Thing]
+
+[justification]
+
+### Expected Consequences <!-- optional -->
+
+* List of unrelated outcomes this decision creates.
+<!-- Positive, negative, and/or neutral consequences, as lll of them affect the team and project in the future. -->
+
+## More Information <!-- optional -->
+
+<!-- * Resources reviewed as part of making this decision -->
+<!-- * Links to any supporting documents or resources -->
+<!-- * Related PRs -->
+<!-- * Related User Journeys -->